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HOW TO RAISE 

LK-WOKMS. 



I 



LIEF MANUAL OF INSTRUCTIONS, 



■ 



ABRIDGED FROM 



BULLETIN NO. 9 OF THE DIVISION OF ENTOMOLOGY, 



BY 



PHILIP WALKER, 

CHIEF OF THE SILK SECTION. 



iHED BY AUTHORITY OF THE SECRETARY OF AGRICULTURE. 



WASHINGTON : 

GOVERNMENT PRINTING OFFICE. 
189 0. 



U.S. DEPARTMENT OF AGRICULTURE. 

SILK SECTION. 
BULLETIN No. 1. 



HOW TO EAISE 

SILK-WOEMS. 



A BRIEF MANUAL OF INSTRUCTIONS, 



ABRIDGED FROM 



BULLETIN NO. 9 OF THE DIVISION OF ENTOMOLOGY. 



BY 

PHILIP WALKER, 

CHIEF OF THE SILK SECTION. 




PUBLISHED BY AUTHJRITY OF THE SECRETARY OF AGRICULTURE. 



WASHINGTON : 

GOVERNMENT PRINTING OFFICE. 
1890- 






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<b« 






y 



LETTER OF TRANSMITTAL. 



U. S. Department of Agriculture, 

Silk Section, 
January 27, 1890. 
Sir: I have the honor to hand you herewith Bulletin No. 1, of this 
Section. It is essentially an abridgment of Bulletin No. 9, of the 
Division of Entomology, " The Mulberry Silk- Worm," and has been pre- 
pared in response to an unquestionable need for something of a pre- 
liminary nature which should not confuse beginners with the intricacies 
of the industry. It is for beginners only that this pamplet is intended. 
For adepts something even more complete than the Entomologist's 
manual seems to me to be needed and I have such a work in hand. 
Yours respectfully, 

Philip Walker, 

Chief of the SilJc Section. 
Hon. J. M. Busk, 

Secretary of Agriculture. 

3 



HOW TO RAISE SILK-WORMS. 



THE SILK-WORM AND ITS FOOD. 

The ordinary silk of commerce is produced by the Chinese silk- worm 
(Bombyx mori), which in its natural state, as well as in most countries 
where the worm has been domesticated, feeds upon the leaf of the mul- 
berry tree. The life of the insect may be divided into four epochs : — the 
egg, the worm, the chrysalis, and the moth. Early in the spring, at 
about the time the mulberry leaves bud out, the eggs hatch and from 
each issues a small worm about one-eighth of an inch long, covered 
with short black hairs. During the four or five weeks ensuing the silk- 
worm spends the greater portion of its time in feeding and, growing 
rapidly, attains a length of about three inches. Having reached its 
full size the worm ceases to eat and, finding some suitable place upon 
which to spin its cocoon, it commences to throw out a thread of silk 
which it forms into a peanut-shaped pod destined to protect the insect 
from the inclemency of the weather while it undergoes the transforma- 
tions first into a chrysalis and then into a moth. About three weeks 
after the final formation of the cocoon both of these transformations 
•will have been completed and the insect will issue in its adult form as 
a small whitish moth whose only function is to assist in the reproduc- 
tion of its species. Silk raisers have generally only to do with that 
epoch which covers the time from the hatching of the egg to the com- 
pletion of the cocoon. The production of the eggs and the reeling and 
the utilization of the cocoon for commercial purposes are parts of other 
industries a knowledge of which is not necessary to the persons who 
rear the worms and produce the cocoons. 

This second epoch of the insect's life is divided into five different 
ages. These ages are separated by what are called molts, when the 
worm sheds its skin. This shedding of the skin is necessitated by 
the rapid increase in size of the insect, the original skin not possessing 
sufficient elasticity to allow for its growth, and it takes place four times 
with the ordinary races. The form and size of a full grown silk-worm 
are seen in Fig. 1. 

5 



It has been said that the silk-worm generally feeds upon the leaves 
of the mulberry tree. While there can be no doubt that the white mul- 
berry tree, in some one of its differeut varieties, forms the most advan- 
tageous food which can be used for the silk- worm, it has been discov- 
ered that the leaves of other plants may be employed with a great de- 
gree of success. The most important of these plants and the only one 
known in the United States is the osage orange, which is used very 




Fig. 1. Full grown silk-worm. 



largely throughout certain portions of the country for the formation of 
hedges on our large farms. The osage orange plant is very thorny and 
its thorns injure the fingers of persons picking the leaves. When the 
leaves are gathered, however, the results obtained from feeding them 
to the worms are excellent. But, as economy in gathering the leaves 
is of great importance to the silk-grower, it would hardly be advisable 
to plant the osage orange with the express purpose of using it for rear- 
ing silk-worms. 

The mulberry tree, on the other hand, while naturally bushy, may 
be so trained as to greatly facilitate the gathering of the leaves, and 
persons who intend to follow the culture of silk for any length of time 
are earnestly counseled to put in the necessary number of these plants. 
For those, however, who have osage orange at their disposal, and who 
are desirous, as are so many of the wives and daughters of the farmers 
of the United States, of experimenting with silk worms, it is deemed 
advisable that they should use the leaves of the osage orange, only 
planting mulberry trees when, as I have said, they have decided to con- 
tinue to follow the industry. After the second molt it will be better not 
to try to pick the osage leaves, but rather to cut off small twigs with 
the leaves on them and give them to the worms altogether. The suc- 
culent terminal leaves should not be fed after the third molt, as they 
are apt to breed disease, but should be cut off before the twigs are 
given to the worms. Persons not having enough mulberry, and intend- 
ing to use osage orange in connection with it, had better save the mul- 
berry for the last age, the most critical part of the worm's life. 

IMPLEMENTS NECESSARY TO SILK RAISING. 

For the small amount of worms raised during the first season a series 
of tables like those shown in Fig. 2 will be all that is necessary. These 
are made movable so that they can be taken down and put away when 



not in use. The tables themselves can be covered either with slats or 
with wire netting such as is currently used in making chicken-coops. 
The latter can be obtained for about li cents per square foot in small 
quantities, or about 50 cents for each table. Such tables as have been 




Fig. 2. — Standard for holding shelves. 

mentioned are shown in Figs. 3 and 4. They should be 4 feet wide and 
8 feet long. These tables should be covered with large sheets of un- 




Fig. 3. — Frame covered with slats. 




Fig. 4.— Wire-work shelf. 



printed paper before the worms are placed upon them. All lumber 
used should be thoroughly seasoned and dry. 



^ 8 

The litter left by the worms after feeding should be cleared away 
systematically, and, as far as possible, without handling the worms. 
This is done by means of perforated paper. During the second age 
this paper is perforated with holes about a quarter of an inch in diame- 
ter, the size of the sheets being, for convenience, about 12 by 18 inches. 
In the other ages the size of the holes increases in proportion to the 
size of the worms until for the last age they are about seven-eighths of 
an inch across. For the third, fourth, and fifth ages the paper is usu- 
ally cut about 18 by 24 inches. To clean away the litter with this 
paper we must place it over the worms and sprinkle a copious supply 
of leaves upon it. The worms will come up through the holes in the 
paper to reach the new leaves, and, when the greater part of them 
have thus appeared, the paper, with the worms and leaves upon it, can 
be moved to another table. Such worms as remain on the litter can be 
transferred by repeating the operation. The litter left on the table can 
then be cleared away, and this should be done without raising any more 



ooooooooo 
ooooooooo 
ooooooooo 








Fig. 5 — Perforated paper, showing ths sizes of the perforations in the second and fourth ages. 



dust than is necessary. Fig. 5 shows the perforations used during the 
second and fourth ages. A small piece of mosquito netting will suffice 
for these transfers at the birth of the worms and during the first age. 

In gathering mulberry leaves for feeding the worms it will be found 
convenient to have a bag (Fig. 6), which may be attached like an apron 
around the waist. Two such bags can be made from an ordinary meal 
sack. In gathering osage orange leaves, however, the twigs and thorns 



prevent their being easily shoved into the bag, and it is therefore better 
to use baskets. 




Fig. 6. — Bag for gathering mulberry leaves. 

Every rearing-room should have a thermometer. One that will be 
good enough for the purpose can be purchased anywhere for half a 
dollar. 



SILK-WORM EGGS : HOW TO WINTER AND HATCH THEM. 

As has been said in the introduction this book is intended only for 
beginners in silk culture and some of the niceties of the industry are 
therefore intentionally neglected. Persons who have never reared silk- 
worms had better confine themselves to beginning with a small quan- 
tity. One-quarter of an ounce of eggs will be amply sufficient. But, 
while the quantity should be thus restricted, in order that the labor 
involved to inexperienced persons may not be so great as to prevent 
their observing closely all the changing phases of the silk-worm's life, 
it is a matter of the greatest importance that the eggs obtained should 
be of the best quality and of such a race that the cocoons raised may be 
easily marketed. Reliable dealers, whose reputation has been made by 
the superior quality of the eggs which they sell, are the only ones who 
should be dealt with. There are about 36,000 silk-worm eggs in an 
ounce ; the quarter of an ounce recommended for beginners would, 
therefore, contain about 9,000. 

These eggs may be obtained either in the spring, just before the time 
to begin the feeding, or early in the winter. In the latter case it is nec- 
essary that the eggs should be kept in such a manner that they be not 
injured or allowed to hatch until the leaves are ready to furnish food 
for the worms. There are but few requisites for the careful wintering 
of silk-worm eggs, the principal ones being that they should be kept 
cool and dry. For this purpose they may be placed in a cold, dry cellar, 
having preferably a northern exposure. It is better, however, for be- 
ginners to obtain their eggs in the spring, so that any danger which 
might arise from their hatching too early will be avoided. When the 
leaves begin to bud out the eggs should be brought into a warm room 
aud left in the open air. They should not be exposed to direct sunlight^ 
nor should they be too strongly subjected to the artificial heat of a stove. 
On the other hand they must not be placed in a room which becomes 



10 

cold during the night. If the eggs have been uniformly kept during the 
winter in a very cold place it will sometimes take from two to three 
weeks for them to hatch out. If, however, the degree of cold has not 
been so great they will hatch out in four or five days. In preparing the 
eggs for hatching it is better to spread them out very thiuly ou a sheet 
of clean paper, and prevent any vermin (such as roaches) from approach- 
ing them. 

THE REARING OF THE WORMS. 

When the silk- worm issues from the egg it is about one-eighth of an 
inch long and covered with black hairs. As the worm grows the hairs 
separate and the worm loses its dark color and becomes a rosy white. 

When the first worms appear they should be covered with a small 
piece of mosquito netting upon which should be scattered a few leaves 
and buds. The netting with the worms and the leaves upon it can 
then be removed to the table upon which they are to be raised, this 
operation being continued until the majority of the worms have hatched. 
Under favorable circumstances this will take from three to four days. 
Silk-worms grow more rapidly when kept in a warm place than when 
in a cool one. It is well known, too, that a room is always warmer 
at the ceiling than at the floor. If, therefore, we place the worms 
first born on the lower table and those born later above them, giving 
the last an additional meal daily, it will be found that they will reach 
the first molt at about the same time. 

Those which hatch out after the fourth day should always be thrown 
away, as they are undoubtedly weaker than the more advanced worms, 
and being consequently more subject to disease, may injure the first in- 
sects if raised with them. It is also sometimes advisable to throw away 
the more vigorous ones which are born ou the first day. The reason 
given for this is that they will be so much ahead of the others as to in- 
terfere with the regularity of rearing. If, however, the instructions 
given above for equalizing the worms are followed this irregularity can 
be overcome and the size of the worms easily regulated later. 

The worms are fed by scattering the leaves over them, care being 
taken to spread it evenly, so that all may be served alike. The worms 
during the first age should be fed about six light meals daily, the 
first early in the morning and the last late at night. During this and 
the next age the leaves should be chopped fine, as the worm eats only 
on the edge of the leaf, and it is important, in the interests of economy, 
to make as many of these edges as possible. In silk raising good and 
systematic habits are as important as elsewhere, and regularity in 
feeding is one of the most important of them. Arrange the hours for 
feeding the worms so that about equal lengths of time shall separate the re- 
pasts, and then stick to them. Neglected silk-worms will never pay for the 
trouble they cause. 

The number of meals may be reduced to five during the second age 



11 

and to four during the last three. Retain the habit, however, of giving 
the first early in the morning and the last late at night. 

It is only by experience that one can learn just what amount of food 
should be given to the worms. It may prove dangerous to feed them 
too copiously, as in the first ages the'worms may become buried and 
lost in the litter, while later the massing of food in an attempt to sat- 
isfy their ravenous appetites may cause it to ferment and become pro- 
ductive of disease. In general they should be given all they will eat. 
The first meal after the fourth molt should, however, be light, as the 
worm at that time possesses a ravenous appetite and is apt to over- 
eat itself. After this the meals should be very plentiful, as it is at this 
time that the worm fills its silk ducts, and if deprived of a full 
supply of food it will make a poor and feeble cocoon. 

Great care should be taken to pick the leaves for the early morning 
meal the evening before, as when picked and fed with the dew upon 
them they are more apt to induce disease. Indeed, the rule should be 
laid down to never feed wet or damp leaves to your worms. In case the 
leaves must be picked during a rain they should be thoroughly dried 
with a cloth before being fed ; on the approach of a storm it is always 
well to lay in a stock of food, which should be kept from heating by 
occasional stirring. % 

During the first and most delicate age the worm requires much care 
and watching. As the 5th or 6th day approaches signs of the first molt 
begin to be noticed. The worm begins to lose appetite, grows more 
shiny, and generally wanders to an unencumbered spot where it may 
shed its skin in quiet, and thus often gets hidden and buried under the 
superimposed leaves. The old skin begins to break away just above 
the head * making at first a dark-red triangular spot. The worm, in 
its pain, throws up the forward part of the body as shown in Fig. 7. 
When the molt is completed and the 
skin has been cast, the head appears 
a much lighter brown and somewhat 
swollen, and the legs seem drawn up 
and of little use. These symptoms 
soon disappear, however. When the 
first worms show these signs of molt- 

° Flu. 7. Silk worm during the fourth molt. 

ing, food should be given more spar- 
ingly and the meals should cease altogether as soon as the most for- 
ward worms awaken. When the time for the molt is near, say during 
the fourth day, it will be well to clear away the litter so that the worms 
may pass the crisis on a clean bed. 

Some will undoubtedly undergo the shedding of the skin much more 
easily and quickly than others, but no food should be given to these for- 
ward individuals until nearly all have completed the molt. This serves to 

* Only the dark-brown shell-like muzzle constitutes the head. 




12 

keep the batch together, and the first ones will wait one or even two days 
without injury from want of food. It is, however, unnecessary to wait 
for all, as there will always be some few which cast their skins some 
time after their companions. These should either be set aside and kept 
separate or destroyed, as they are usually the most feeble and most 
inclined to disease ; otherwise the batch will grow more and more 
irregular in their molting and the diseased worms will contaminate the 
healthy ones. It is really doubtful whether the silk raised from these 
weak individuals will pay for the trouble of rearing them separately 
and it will be better perhaps to destroy them. It is very important in 
the interest of that system whose value has been urged to keep each 
batch together and cause the worms to molt simultaneously. When 
this is done the work will be much simplified and much time econo- 
mized. 

As soon as the great majority have molted they should be covered 
with the perforated paper and fed. As they grow very rapidly after 
each molt the space which they occupy should be increased. This is 
readily done by removing the perforated paper when about half of the 
worms have risen and replacing it by an additional one. The space 
allotted to the worms should, of course, be increased proportionately 
with their growth. 

The same precautions should be observed in the three succeeding 
molts as in this first one. The second and third castings of the skin take 
place with but little more difficulty than the first one, but the fourth is 
more laborious, and the worms not only take more time in undergoing 
it but more often perish in the act. At this molt it is better to give the 
more forward individuals a light feed as soon as they have completed 
the change, inasmuch as it is the last molt and but little is to be gained 
by the retardation, whereas, as has been said, it is important to feed 
them all that they will eat during this age. It would too be found in- 
convenient if all the worms were to arrive at the spinning period to- 
gether, as extra assistance would be required to put in place the brush 
on which they spin their cocoons. 

As regards the temperature ot the rearing -room, great care should be 
taken to avoid all sudden changes from warm to cold or cold to warm. 
A temperature of 75 or 80 degrees will usually bring the worms to the 
spinning point in the course of thirty to thirty-five days after hatching, 
but the rapidity of development depends upon a variety of other causes, 
especially upon the quality of leaf. If the rearing lasts more than thir- 
ty-Jive days from hatching to spinning, there can be no doubt that the 
icorms have not been sufficiently fed, or that the rearing room has been too- 
cold. If it can be prevented the temperature should not be permitted 
to rise very much above 80 degrees. The air should be kept pure all of 
the time, and arrangements should be made to secure a good circulation 
without subjecti?:g the worms to draughts. Great care should be taken 
to guard against the incursions of ants and other predaceous insects, 



13 

which would make sad havoc among the worms were they allowed an 
entrance, and all through the existence of the insect, from the egg to the 
moth, rats and mice are on the watch for a chance to get at them, and 
are perhaps to be feared most among the enemies of the silk -worm. 

Too much can not be said in favor of giving the worms plenty of 
room. Every one -should be free to move easily without incommoding 
its fellows. We should therefore allow the issue of an ounce of eggs 
during the first age from 10 square feet at the beginning to 30 square 
feet at the end of the age, daily extending the space occupied by them 
by spreading their food over a greater table surface. In the second 
age they should spread in the same manner so as to cover from 50 to 75 
square feet, in the third from 100 to 160 square feet, and in the fourth 
from 200 to 320 square feet. Entering the last age, spread over 430 
square feet of surface, they should gradually be extended until they 
occupy at the spinning period 640 square feet. It need hardly be said 
that when the worms have been decimated by disease the surface oc- 
cupied by them need not be so extensive. 

The litter of the worms should be cleared away in the manner de- 
scribed before and after each molt, and once each at about the middle 
of the third and fourth ages. While the worms are small the litter 
dries rapidly and may (though it should not) be left for several days on 
the table with impunity ; but he who allows his tables to go uncleaned 
for too long a time during the two last ages will suffer in the disease 
and mortality of his worms just as they are reaching the spinning 
point. 

The only disease which American silk raisers need fear at present is 
called flaccidity. It is caused by feeding the worms wet or damp leaves 
or perhaps by thunder storms and other bad weather. The worm at- 
tacked with it dies and turns brown and then black. The disease is 
caused by the food failing to digest and often kills off a whole lot of 
worms with surprising rapidity. There is no known way of stopping it 
once it attacks the worms, but it may be generally avoided by follow- 
ing carefully the instructions given above. 

These, summed up, may be reduced to the following rules: 

(1) Keep the worms of each lot uniform in size so as to insure their 
molting simultaneously. 

(2) Let them be systematically supplied with fresh food except during 
the molting periods. 

(3) Give the worms plenty of room so that they may not crowd each 
other. 

(4) Let there be plenty of fresh air and as uniform a temperature as 
possible, but have no draughts. 

(5) Use every means to insure cleanliness. 

(6) Never feed damp or wet leaves. 

The last four are particularly necessary during the fourth and fifth 
ages. 



14 



PREPARATIONS FOR SPINNING. 

• 

With eight or ten days of busy feeding, after the last molt, the worms 
will begin to lose appetite, shrink in size, become restless, and throw 
out threads of silk. The arches for the spinning of tbe cocoons must 
now be prepared. These can be made of dry twigs 2 or 3 feet long, set 
up upon the shelves over the worms and made to interlock in the form 
shown in Fig. 8. The feet of each arch should be only about a foot 
apart. 




Fig. 8. — Method of constructing arches upon which the cocoons are span. 

The temperature of the room should now be kept above 80 degrees as 
the silk does not flow so freely in a cool atmosphere. The worms will 
one by one mount into the branches and commence to spin their cocoons. 




Fig 9.— Cocoon. 



They will not all, however, mount at the same time, and those which 
are more tardy should be fed often, but in small quantities at a time, 
in order to economize the leaves, as almost every moment some few 



15 

will quit and go up into the arches. There will always be a few which 
fail altogether to mount and prefer to spin on the tables. 

As the worms begin to spin they should be carefully watched to guard 
against two or three of them making what is called a double or treble 
cocoon, which would be unfit for reeling purposes. Whenever one worm 
is about to spin too near another it should be carefully removed to 
another part of the arch. In two or three days the spinning will have 
been completed, and in six or seven the chrysalis will have been formed. 
Fig. 9 shows a medium sized fine cocoon spun by a worm of a yellow 
annual race. 

PREPARING THE COCOONS FOR MARKET. 

Eight days from that on which the spinning fairly commenced it will 
be time to gather the cocoons. The arches should be carefully taken 
apart and the spotted or stained cocoons first removed and laid aside. 
Care should be taken not to stain the clean cocoons with the black 
fluids of such worms as may have died and become putrid, for there are 
always a few of these in every cocoonery. Too much care can not be 
taken to remove the soft or imperfect cocoons as, if mixed with the firm 
ones, they would be crushed aud soil the latter with their contents. 
The floss surrouudingthe cocoons should be thoroughly remove! before 
stifling. 

In most silk-producing countries the persons who raise the cocoons 
sell them to the reeling establishments before it becomes necessary to 
kill the chrysalis, as these establishments have better facilities for this 
work than are to be found in private families. If, however, the reeling 
is done by the raiser, or some time must elapse before the cocoons can 
be sent to a reeling establishment, some means must be used to stifle 
them before they are injured for reeling purposes by the egress of the 
moth. This can best be done by steaming them. 

The following apparatus has been used at the Department and found 
satisfactory: It consists of a tin reservoir (Fig. 10) about one-third 
filled with water. Slightly above the surface of the water is a movable 
perforated partition B, inteuded to prevent spattering during ebulli- 
tion. The upper portion contains a perforated pan for holding the co- 
coons while all is tightly closed by a cover. Cocoons may be thoroughly 
stifled by exposure in this apparatus over boiling water for twenty min- 
utes. It will be seen, too, that much the same apparatus may be con- 
trived by the use of a deep kettle, into which is set an ordinary colan- 
der full of cocoons. It is well to avoid, however, so filling the kettle 
with water that it will splash upon the cocoons in boiling, as they 
should be subjected only to the action of steam. The apparatus is 12 
inches in diameter and 13 inches deep and will stifle from 3 to 4 pounds 
of cocoons at a time. 

Cocoons submitted to this process should be thoroughly dried to 
prevent their molding. This takes about three months. They should 



16 

be spread out in layers not more than 4 or 5 inches deep and should be 
stirred every few days at first and Iqss frequently later. They should 
be guarded from rats and mice which eat through the cocoon and de- 
vour the chrysalis. When thoroughly dry they can be packed in strong 




Fifi. 10. — Simple stifling apparatus. 

sacks and shipped to the filature. It is not necessary to pack dry co- 
coons in boxes which form the great proportion of the weight of the 
packages and greatly increase the cost of transportation. Burlaps, 
such as used in packing furniture, will protect dry cocoons sufficiently 
for long journeys by freight trains. 



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